1. Field of the Invention
The present invention relates generally to portable radio terminal equipment, and in particular, to compact, lightweight portable radio terminal equipment with a better radiation efficiency to thereby reduce harm to human bodies caused by radiation.
2. Description of the Related Art
There is a trend in mobile communication technology to provide increasingly more compact, lightweight radio terminal equipment in accordance with user preference. In general, the length of existing portable radio terminal equipment does not exceed λ/4, where λ represents the received electromagnetic wavelength corresponding to the operating frequency. Since portable radio terminal equipment uses electromagnetic waves for communication, a radiation efficiency is an important factor in increasing call quality.
FIG. 1A is a front view of a conventional portable radio terminal having a conductive printed circuit board (PCB), and FIG. 1B is a side view of the conventional potable radio terminal.
Referring to FIGS. 1A and 1B, a dipole antenna 100 uses a body 120 as a ground. The dipole antenna 100 has an efficiency and a radiation pattern, which varies according to its length. The dipole antenna 100 radiates the maximum signal when the length is λ/2, and incurs a radiation loss when the length is below λ/2.
FIG. 2 illustrates the distribution of a radiation current when the total length of the body and the antenna of the portable radio terminal is below λ/2. In FIG. 2, the total length of the body and the antenna is λ/2−a. As shown, the equivalent circuit and the radiation current distribution includes a radiation loss, as represented by a dotted line.
FIG. 3 illustrates the distribution of a radiation current when the total length of the body and the antenna of the portable radio terminal is λ/2. The total length of the body and the antenna is λ/2, thus the equivalent circuit and the radiation current distribution includes no radiation loss.
In contrasting the radiation current distribution of FIGS. 2 and 3, it is evident that a radiation loss occurs when the total length of the body and the antenna is below λ/2, whereas the radiation loss does not occur when the total length is λ/2. However, this factor places a limitation on the compactness of the portable radio terminal, which is contrary to the current user preference.
Therefore, a technique capable of maintaining a good radiation efficiency, while reducing the total size of the body and the antenna to λ/2 and below is needed.